The utility of incorporating an insulating lid onto a molten metal transport vessel is not new and is becoming increasingly common as its advantages become more widely known and its implementation becomes easier. These advantages can be summarized under the headings of better heat retention, reduced slag solidification and build up, and improved life of refractories. In elementary implementations, the lids are placed and removed by factory cranes whenever needed. Although achieving the aforementioned advantages, these implementations have the imposed drawbacks of reducing cycle times, and requiring crane resources that could be utilized elsewhere.
A known apparatus for removing and replacing a lid on a metallurgical ladle is described in U.S. Pat. No. 4,834,346 (Heyer et al.) The technology introduced therein is a hinged ladle lid system that requires minimal crane time and has minimal impact on cycle time. The system automatically removes/replaces a hinged insulating ladle lid in process as the ladle is in transit. The method employed to achieve this is a three finger structure that mates with corresponding lifting pins on the lid as the ladle moves underneath. The relative movement of the ladle car with respect to the fingers will remove or replace the lid depending on the direction of travel of the ladle car.
This technology, as set forth in Heyer et al., successfully addresses the aforementioned drawbacks of a standard insulated lid system but manifests another inherent limitation in its implementation. When the fingers are acting on the lid, the hinge design dictates a single orientation of the lid with respect to the fingers. Also, the lifting motion of the lid is driven by the movement of the ladle car itself. Consequently, each direction of travel of a ladle car is inexorably tied with a single lid action. For example a ‘forward’ ladle car movement can produce only a lid removal and ‘reverse’ ladle car movement can produce only a lid replacement. A ‘forward’ ladle car movement is defined such that the ladle hinge is trailing in the direction of movement. A ‘reverse’ ladle car movement is defined such that the hinge is leading in the direction of movement.
Accommodating this ‘reverse’ orientation scenario with retractable fingers as set forth in Heyer et al. results in unacceptable increases in cycle time and larger demands on plant space. This method requires the ladle to move under and past retracted fingers, come to a stop and reverse direction back through the now lowered fingers. After the lid is removed the ladle must again come to a stop beyond the fingers, reverse direction, and travel under and past the again retracted fingers to the process station. After returning from the process station, the same lengthy sequence of finger retractions and ladle reversals is needed to retrieve the lid.
A sideways ladle orientation, is one that occurs less frequently, but is also unable to be acted upon by the passive finger method of Heyer et al. A separate method has been used previously to address this situation. The solution employs a frame with hooks lowered and raised on cables. This method is only used in this sideways orientation situation as it relies on the positioning tolerance afforded by the lifting pins when in that orientation. Conversely, positioning tolerances required to use this method in other orientations are too tight for most applications.
For new plant constructions, ladle orientation/directionality issues can usually be avoided by developing the layout to accommodate the requirements of the normal non-retracted finger method. However space limitations remain a salient issue for all plants, and other ladle orientations/directions may not be avoidable, even in new plants.
In pre-existing steelmaking plants, space considerations are compounded by more prevalent occurrences of the ladle orientation challenges highlighted above. Thus it is desirable to have a supplemental method of automatically removing the lid that is not contingent on the directionality of the ladle car and/or orientation of the ladle, and that delivers this functionality swiftly and in a package requiring minimal plant space.